Homeopathy was first conceived in the late 18th century by German physician Samuel Hahnemann. Hahnemann noticed a similarity between the symptoms created by giving undiluted cinchona bark extract to healthy individuals and the symptoms of malaria, which the very same cinchona bark had been conventionally used to heal. ^[1] Hahnemann concluded that, to be effective, drugs should produce the same sorts of symptoms in healthy individuals as are being experienced by the patient with the illness that the drug is supposed to treat ^[2]. The homeopathic practitioner repeatedly dilutes the chosen substance, and, at each stage of the dilution, shakes it. Finished homeopathic remedies are so dilute they contain few or even no molecules of the original substance, ^[3] a fact which is central to criticism of the tradition by physical and biological scientists. Homeopaths contend that the shaking causes an imprint (or " memory") of the diluted substance upon the vehicle (the diluting water or alcohol itself); ingesting the resulting remedy harmonizes and re- balances a theorized vital force in the body, thus restoring health.

Claims for the medical efficacy of homeopathic treatments have been repeatedly rejected as unsupported by the collective weight of scientific and clinical studies. ^{[4] [5] [6] [7]} Homeopathic philosophy has been characterized as strikingly at odds with the laws of chemistry and physics, since it postulates that extreme dilution actually makes drugs more powerful (by enhancing, homeopaths believe, their "spirit-like medicinal powers" ^[8]). Scientists have asserted that there is no evidence of water or alcohol retaining any sort of imprint of a substance that was once dissolved in it, and that any positive effects of homeopathic treatments must be due simply to the placebo effect. ^{[9] [1] [4] [5]} Furthermore, some health advocates have accused homeopathic practitioners of giving false hope to patients who might otherwise seek conventional treatments. ^{[10] [11]} Many have pointed to meta-analyses which, they contend, confirm the fact that any benefits of taking homeopathic medicine are due to the placebo effect; apparently positive studies of homeopathy have been criticized as being flawed in design. These findings, they say — along with the common practice of homeopaths to proscribe their patients from receiving conventional medical treatments for a given malady while being treated for it with homeopathy — argue for labeling homeopathy as a brand of quackery, ^{[12] [13] [14]} reliance on which could effectively endanger the patient's health.